The present invention relates to a device for monitoring lubrication of large diesel engines or other engines having large pistons in a plurality of driving spaces. The monitoring device is of the type which includes measuring receiver connected to one or more driving spaces to suck oil mist from the latter into a test channel where a li9ht barrier senses the concentration of the oil mist and generates electrical signals proportional to the measured concentration. The electrical signals from all measuring receivers are supplied via a common multiple conductor cable to a central electrical evaluation unit provided with control means which in the case of an excessive concentration of the oil mist detected in at least one measuring receiver generates an alarm signal which throttles or turns off the corresponding engine. The suction of the oil mist into the test channels of respective receivers is performed by a central vacuum pump connected to the receivers by a common underpressure conduit.
Lubrication monitoring devices of this kind are employed mostly on heavy duty diesel engines on vessels in order to prevent damages or explosions in the driving spaces due to malfunction in lubricating systems. Such damages may occur for example in the case when the lubricating film between the sliding surfaces is interrupted and excessive heat developed due to dry friction increases temperature of lubricating oil around the disrupted location to such an extent that the oil evaporates. The oil vapors condense in the lower temperature atmosphere of the driving space in an oil mist whose increasing concentration serves as an indicator in the monitoring device for detecting the beginning of a lubrication damage.
In the prior art oil mist monitoring devices the suction conduits communicating with respective sections of driving spaces of the monitored engine open in the same test channel of the monitoring device provided with the light barrier. In operation, it was necessary to control the feeding of the oil mist from respective sections of the driving spaces one after the other by means of valves and the concentration was consecutively measured in the test channel. Due to the time delay caused by the suction of the oil mist through relatively long suction pipes and time delays due to the sequential interrogation of respective driving spaces, the prior art devices cannot guarantee a timely detection of lubrication failure. This uncertainty is caused particularly due to the fact that all driving space sections of the engine generate also oil mist resulting from spraying of the oil by centrifugal effect of moving parts and are also vaporized in hot regions of the driving spaces during the normal operation whereby continuously a basic oil concentration in the sucked out gas is present. This basic concentration impairs the detection of the additional oil mist concentration generated at the beginning of a lubrication failure. It is necessary therefore to detect as fast as possible the start of a lubrication failure but on the other hand, false alarms which may result due to normal operational situations of the basic oil mist concentration must be under all circumstances avoided inasmuch as an unnecessary inactivation of a drive of a ship might lead to unnecessary hazardous conditions. Moreover, due to long suction pipes the precipitation of oil in lower bends of the pipe cannot be avoided. Such oil depositions reduce the oil mist concentration and may even plug the suction pipes.
In order to improve the oil mist measuring method applicant has already proposed a measuring arrangement in which a separate measuring receiver is assigned to each section of the driving space of the engine and a central electric evaluation unit electrically connected to the receiver. In this manner all driving spaces are simultaneously monitored without any time delay and are immediately compared one with each other in the evaluation unit. Nevertheless, the disadvantage of this arrangement is its relatively complex design requiring the provision of individual installation plans and also the service and maintenance has required highly skilled electrical and mechanical workers and high installation and maintenance expenditures.